Journal of Geosciences, 67 (2022), 289–297

DOI: 10.3190/jgeosci.359

Original paper

Stibioústalečite, Cu6Cu6(Sb2Te2)Se13, the first Te–Se memberof tetrahedrite group, from the Ústaleč, Czech RepublicJiří SEJKORA1*, Jakub PLÁŠIL2, Emil MAKOVICKY3
Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Praha 9 - Horní Počernice, Czech Republic;
jiri.sejkora@nm.cz
2Institute of Physics of the CAS, v.v.i., Na Slovance 2, 182 21 Praha 8, Czech Republic
3
Institute for Geoscience and Natural Resources Management, University of Copenhagen, Østervolgade 10, DK-1350,
Copenhagen K, Denmark*
Corresponding author
1

Stibioústalečite, Cu12(Sb2Te2)Se13, was approved as a new mineral species from the Ústaleč mine, 15 km west ofHoražďovice, SW Bohemia, Czech Republic. It occurs as metallic anhedral grains up to 0.1–0.3 mm in size, dark grey incolor, in a calcite gangue. It is directly associated with hakite-(Hg), berzelianite, the not-yet approved phase Cu12(As2Te2)
Se13 and uraninite. Stibioústalečite is brittle, with an indistinct cleavage and a conchoidal fracture; the calculated density
is 5.676 g/cm3. In reflected light, stibioústalečite is isotropic, and grey in color; internal reflections were not observed.
Reflectance data for the four COM wavelengths in air are [λ (nm): R (%)]: 470: 33.3; 546: 33.2; 589: 33.1; 650: 33.0.
Electron microprobe analysis for holotype material (grain used for single-crystal X-ray study) gave (in wt. % – average of 7 spot analyses): Cu 34.10, Ag 1.22, Fe 0.04, Zn 0.09, Hg 0.33, Sb 9.39, As 0.70, Te 12.41, S 3.76, Se 37.59,
total 99.63. On the basis of (As + Sb + Te) = 4 atoms per formula unit (apfu), the empirical formula of stibioústalečite isM(2)(Cu5.75Ag0.25)Σ6M(1)(Cu5.93Hg0.04Zn0.03Fe0.02)Σ6.02X(3)(Te2.12Sb1.68As0.20)Σ4(Se10.36S2.55)Σ12.91. The ideal formula is Cu6Cu6(Sb2Te2)
Se13, which requires Cu 33.33, Sb 10.64 Te 11.16 Se 44.87, total 100 wt. %. Stibioústalečite is cubic, I4̄3m, with unit-cellparameters a = 10.828(4) Å, V = 1269.6(9) Å3, Z = 2. The crystal structure of stibioústalečite was studied by single-crystal X-ray diffraction data and it is isotypic with other members of the tetrahedrite group. The mineral is named after
its type locality Ústaleč and its chemical composition, being the (Sb/Te) end-member in the possible ústalečite series.
Keywords: stibioústalečite, new mineral, tetrahedrite group, chemical composition, Ústaleč, Czech Republic
Received: 15 February 2022; accepted: 20 September 2022; handling editor: F. Laufek

1. Introduction
Tetrahedrite group minerals are the most common sulfosalts in different kinds of hydrothermal ore deposits.
They form a complex isotypic series, with formula
M(2)
A6M(1)(B4C2)Σ6X(3)D4S(1)Y12S(2)Z, characterized by homoand heterovalent substitutions, representing an interesting
link between mineralogy and ore geochemistry (Biagioni
et al. 2020a). The classification and nomenclature of thetetrahedrite group minerals, in keeping with the current
IMA-accepted rules, was recently published by Biagioni
et al. (2020a). The general structural formula of minerals
belonging to this group can be written as M(2)A6M(1)(B4C2)Σ6
X(3)
D4S(1)Y12S(2)Z, where A = Cu+, Ag+, □ (vacancy), and(Ag6)4+ cluster; B = Cu+, and Ag+; C = Zn2+, Fe2+, Hg2+,
Cd2+, Ni2+, Mn2+, Cu2+, Cu+, and Fe3+; D = Sb3+, As3+,
Bi3+, and Te4+; Y = S2–, and Se2–; and Z = S2–, Se2–, and □(Biagioni et al. 2020a).
This compositional diversity is reflected in the relatively large number of mineral species belonging to thisgroup that has been approved by the Commission on
New Minerals, Nomenclature and Classification of theInternational Mineralogical Association (IMA-CNMNC).
In addition to the eleven mineral species redefined in
Biagioni et al. (2020a), thirteen new mineral species havebeen described in two years, emphasizing the chemicalvariability of this isotypic group.
The Te-rich members of tetrahedrite group have been
known for a long time. The first descriptions of goldfieldite were given by Sharwood (1907) and Ransome (1909),
Thompson (1946) proved it to show isotypic relations
with tetrahedrite. Kato and Sakurai (1970) and Kalbskopf(1974) found that Te does not substitute for S but behaves
similarly as Sb and As in the crystal structure of tetrahedrite or tennantite. Several authors have debated the actual
definition of goldfieldite (e.g., Trudu and Knittel 1998) andit was finally solved in the nomenclature of the tetrahedrite
group by Biagioni et al. (2020a). Increased Se-contents in
Te-rich members have so far been known only in samples
from the epithermal Au deposits at Kamchatka, Russia(Spiridonov and Okrugin 1985; Pohl et al. 1996; Spiridonov et al. 2014), and from the Wild Dog epithermal Au
system on Bougainville Island, Papua New Guinea (Noviello 1989), and they do not exceed 3.0 apfu Se.
www.jgeosci.org

Jiří Sejkora, Jakub Plášil, Emil Makovicky

a)

b)
H
U

B
200 mFig. 1 Stibioústalečite (U) as anhedral grains up to 0.3 mm in length in calcite gangue in association with hakite-(Hg) (H) and berzelianite (B);a – reflected light microscopy (partly crossed polars); b – BSE photo.

Actually, new chemical data available for samples
from locality Ústaleč (western Bohemia, Czech Republic) show Se-dominant composition with (As + Sb)/Te
atomic ratios close to 1, with Sb > As, i.e., close to theend-member formula Cu12(Sb2Te2)Se13. It allowed thesubmission of a proposal to the IMA-CNMNC to givea definition of the Se-analogue of stibiogoldfieldite. The
mineral and its name have been approved (IMA 2021071). Stibioústalečite ("stibio-oostaletchite") is named after its type locality Ústaleč and its chemical composition,
being the (Sb/Te) end-member in the possible ústalečite
series. The name is in analogy with the proposal of
Biagioni et al. (2020a) for the goldfieldite series. Holotype material of stibioústalečite (polished section)
is deposited in the collections of the Department ofMineralogy and Petrology, National Museum in Prague,
Cirkusová 1740, 19300 Praha 9, Czech Republic, under
the catalog number P1P 7/2021.

2. Occurrence
Stibioústalečite was found at the small Ústaleč uranium
deposit, mined by (now abandoned) Ústaleč mine located500 m northeast of the village Ústaleč, 15 km west ofHoražďovice, western Bohemia, Czech Republic (GPScoordinates: 49°19'15.04"N, 13°30'21.40"E). The smallÚstaleč uranium deposit belongs to the Horažďovice
uranium district, similarly to several analogous deposits
and occurrences, including Újezd u Kasejovic, Nalžovské
Hory, Těchonice and others. The hydrothermal uranium mineralization exhibits structural control by theregional Horažďovice fault zone trending WNW–ESE.
The deposit is located in metamorphic rocks of the
Varied Group of the Moldanubian complex at contact
with the Chanovice apophysis of the Central Bohemian
Plutonic Complex (Litochleb et al. 1999). Three main
fault systems are important in the tectonic structure290of the deposit. The first set is represented by mylonite
zones practically free of mineralization, trending E–W
to WNW–ESE, dipping 65–80° to SE. The second groupcontains northeast-trending structures dipping 45–80°
SE, accompanied by two morphological types of uranium
mineralization – vein-zones and so-called contrastingveins. The vein zones 1–15 m thick are represented byzones of crushed rocks carrying numerous carbonate andquartz veins and veinlets showing an en-echelon pattern.
The uranium mineralization in vein zones attains 5 to 80
cm thickness. The predominating contrasting veins are up
to 1 m thick, with vein filling of tectonic clay, carbonates,
quartz and uranium minerals with accompanying sulfides
and selenides. The third group includes vein structures ofcomplicated course, usually 50 cm to 1 m thick. Crushedrocks, carbonates, quartz, fluorite and local uranium
mineralization, usually of uneconomic character, fill thelatter type of veins (Litochleb et al. 1999).
Selenide mineralization of this deposit is tied to whiteor yellowish, post-ore calcite (younger than uranium
mineralization). Selenides penetrate uraninite along
grain interfaces and they overgrow or replace spheroidal
uraninite aggregates at places. Litochleb et al. (1999)
described berzelianite, bukovite, clausthalite, eskebornite,eucairite, ferroselite, hakite, giraudite, chaméanite andumangite there.

3. Physical and optical properties
Stibioústalečite occurs as anhedral grains up to 0.1–0.3
mm in size (Figs 1 and 2), dark grey in color with a grey
streak. It is opaque and luster is metallic. The Mohs
hardness may be close to 3½–4, in agreement with othermembers of the tetrahedrite group. Stibioústalečite isbrittle, with an indistinct cleavage and a conchoidal
fracture. Density was not measured, owing to the small
amount of available material; based on the empiricalStibioústalečite, a new tetrahedrite group mineral from Ústaleč

a)

b)
U

100 mB

Fig. 2 Stibioústalečite (U) as anhedral grains up to 0.2 mm in length in calcite gangue in association with berzelianite (B) and uraninite (white in
BSE); the area of the extracted fragment for the single-crystal study is outlined by red color; a – reflected light microscopy (partly crossed polars);b – BSE photo.

are athabascaite, bukovite, chaméanite, clausthalite,
crookesite, eskebornite, eucairite, klockmannite, umangite, and the not-yet approved “hakite-Cu”. It is of a
low-temperature hydrothermal origin.

Tab. 1 Reflectance data of stibioústalečite from Ústaleč
λ (nm)
400
420
440
460
470
480
500
520
540
546

R (%)
32.8
33.1
33.1
33.2
33.3
33.3
33.3
33.2
33.1
33.2

λ (nm)
560
580
589
600
620
640
650
660
680
700

R (%)
33.1
33.1
33.1
33.1
33.0
33.0
33.0
32.9
33.9
32.9

4. Chemical composition

R (%)

formula and the single-crystal unit-cell parameters, thecalculated density is 5.676 g/cm 3. In reflected light,
stibioústalečite is isotropic. It is grey; internal reflections were not observed. Reflectance values, measured
in the air using a spectrophotometer MSP400 Tidas at
Leica microscope and standard
WTiC (Zeiss 370), with a 100×
objective, are given in Tab. 1 and34
shown in Fig. 3. Stibioústalečite
was identified in samples ofcalcite gangue. It is directly as32
sociated with hakite-(Hg), berzelianite, the not-yet approved“arsenoústalečite” and urani30
nite. Other associated minerals

Chemical analyses were performed using a Cameca
SX100 electron microprobe (National Museum, Prague)
operating in wavelength-dispersive mode (25 kV, 20 nA
and 1 μm wide beam). The following standards and X-raylines were used to minimize line overlap: Ag (AgLα), Au(AuMα), Bi (BiMβ), CdTe (CdLα), Co (CoKα), chalcopyrite(CuKα), pyrite (FeKα, SKα), HgTe (HgMα), NiAs (NiKα,
AsL β), PbS (PbM α), PbSe (SeL α), PbTe (TeL α), Sb 2S 3
(SbLα), Tl(BrI) (TlLα) and ZnS (ZnKα). Peak counting
times were 20 s for all elements and one-half of the peakFig. 3 Reflectance curve for stibioústalečite from Ústaleč. For the sake of comparison, the curves for stibiogoldfieldite(1) from Mohawk mine (Biagioni et al.
2022), stibiogoldfieldite (2) from Goldfield (Criddle and Stanley 1993, p. 208,
described as goldfieldite) and arsenogoldfieldite (3) from Tramway mine (Criddle
and Stanley 1993, p. 209, described as
goldfieldite) are shown.

stibioústalečite
stibiogoldfieldite 1
stibiogoldfieldite 2
arsenogoldfieldite 3

28

26
400

450

500

550

600

650

700

 (nm)
291

Jiří Sejkora, Jakub Plášil, Emil Makovicky

minerals; due to possible vacancies at M(2)A-site in the
Te-rich members, the best approach is (Biagioni et al.
constituent
mean
range
(σ)
2020a, 2022) normalization on the basis of (As + Sb + Te)
Cu
34.10
31.62–35.55
1.37= 4 apfu, taking into account that previous studies (e.g.,Ag
1.22
0.16–3.70
1.34
Johnson et al. 1986) revealed that negligible variations
Fe
0.04
0.00–0.14
0.05
concerning the ideal number of X(3) atoms occur.
Zn
0.09
0.00–0.14
0.05
The general structural formula of the tetrahedrite
Hg
0.33
0.00–0.92
0.36
Sb
9.39
9.09–9.64
0.22
group minerals can be best defined as M(2)A6M(1)(B4C2)
X(3)
As
0.70
0.56–0.97
0.13
D4S(1)Y12S(2)Z (Biagioni et al. 2020a). Analytical data
Te
12.41
11.73–13.12
0.46
for the grain from holotype sample used for the singleS
3.76
3.04–4.44
0.55
crystal study (7 analyses) are given in Tab. 2 and giveSe
37.59
36.44–38.29
0.63
the following formula: (Cu11.68Ag0.25Hg0.04Zn0.03Fe0.02)Σ12.02
total
99.63
(Sb1.68As0.20Te2.12)Σ4(Se10.36S2.55)Σ12.91. On the basis of the crys(σ) - estimated standard deviation
tal structure of goldfieldites (Biagioni et al. 2020a, 2022),
the crystal-chemical formula of stibioústalečite can betime for each background. Other elements, such as Au,
written as M(2)(Cu5.75Ag0.25)Σ6M(1)(Cu5.93Hg0.04Zn0.03Fe0.02)Σ6.02
Bi, Co, Ni and Pb were found to be below the detection
X(3)(Te 2.12Sb 1.68As 0.20) Σ4(Se 10.36S 2.55) Σ12.91. The simplified
limits (0.02–0.05 wt. %). Raw intensities were converted
formula is (Cu,Ag)6(Cu+,Hg,Zn,Fe)6[(Sb,As,Te)2Te2]Σ4
to the concentrations of elements using the automatic(Se,S)13 and end-member formula is Cu6Cu6(Sb2Te2)Se13,“PAP” (Pouchou and Pichoir 1985) matrix-correction
corresponding to (in wt. %) Cu 33.33, Sb 10.64 Te 11.16
software. There are several different approaches for calSe 44.87, total 100.
culating the chemical formula of the tetrahedrite group
The chemical composition
for other grains and samples ofTestibioústalečite from Ústaleč is0given in Tab. 3 and presented
100
in Figs 4 and 5. Besides pre10
vailing stibioústalečite, some90 ústalečite
grains with As > Sb contents
20(Tab. 3) corresponding to the80
not-yet approved end-mem30
ber "arsenoústalečite" were70
also observed in the material studied (Fig. 4); it has the
40
60
chemical formula (mean ofstibioústalečite
arsenoústalečite
11 analyses) M(2)(Cu5.73Ag0.27)Σ6
50
50
M(1)
(Cu 6.17 Fe 0.03 Hg 0.02 Zn 0.01 ) Σ6.53
X(3)(Te
As 1.31 Sb 0.96 ) Σ4 (Se 10.81
60
1.73
40
S 1.79) Σ12.60. The minor Ag contents for all studied grains of
7030ústalečite series are found in
the range 0.03–0.77 apfu and80
20
do not correlate with Sb, Te or S
contents. The determined Me2+
90
10
(Hg + Fe + Zn + Cd) contents inthe minerals of ústalečite series
100
do not exceed 0.35 apfu (Fig.
05a) which are fully in line with
10
20
30
40
50
60
70
80
90
100
Sb 0
As
substitution M(1)Me 2+ + X(3)(Sb/
giraudite series
hakite seriesAs) 3+ = M(1) Cu + + X(3) Te 4+ , pubstibioústalečite - grain used for SCXRD
lished for Te-members of tetrastibioústalečite - other grains
hedrite group with Te contents
Tab. 2 Chemical data for stibioústalečite (grain used for SCXRD)"arsenoústalečite""hakite-(Cu)"hakite-(Hg)292

Fig. 4 Ternary Te–Sb–As graph (at.
unit) for Te-bearing tetrahedrite-groupminerals from Ústaleč.

Stibioústalečite, a new tetrahedrite group mineral from Ústaleč

Tab. 3 Representative chemical analyses for members of ústalečite series from Ústaleč
stibioústalečite
Ag
0.89
0.20
1.87
2.14
0.67
2.33
0.28
0.28
Fe
0.00
0.48
0.00
0.00
0.09
0.00
0.08
0.30
Tl
0.00
0.00
0.45
0.00
0.00
0.00
0.00
0.00
Zn
0.19
0.48
0.20
0.14
0.12
0.15
0.15
0.07
Hg
2.03
0.09
2.03
0.90
0.33
0.81
0.08
0.00
Cu
34.34
37.05
34.71
33.81
34.91
33.91
34.37
35.30
Sb
9.36
11.03
10.87
10.29
6.30
10.06
5.86
5.77
As
4.14
2.19
1.35
1.08
3.50
0.85
3.36
3.53
Se
39.62
32.32
38.33
38.94
41.33
37.91
41.33
40.05
Te
6.71
8.89
8.54
10.32
10.63
10.80
10.96
11.65
S
2.85
5.93
2.36
2.39
1.87
2.38
1.76
2.88
total
100.1398.66 100.70 100.01
99.75
99.20
98.22
99.83
Ag
0.179
0.039
0.398
0.441
0.138
0.484
0.058
0.056
CuA
5.821
5.961
5.602
5.559
5.862
5.516
5.942
5.944
6.000
6.000
6.000
6.000
6.000
6.000
6.000
6.000
ΣA
CuB+C
5.880
6.342
6.940
6.277
6.228
6.434
6.156
6.014
Fe
0.000
0.181
0.000
0.000
0.034
0.000
0.033
0.116
Tl
0.000
0.000
0.051
0.000
0.000
0.000
0.000
0.000
Zn
0.063
0.156
0.069
0.048
0.039
0.051
0.050
0.023
Hg
0.219
0.010
0.233
0.100
0.037
0.090
0.009
0.000
6.163
6.687
7.292
6.425
6.339
6.576
6.248
6.153
ΣB+C
Sb
1.665
1.912
2.050
1.880
1.139
1.850
1.077
1.020
As
1.197
0.618
0.414
0.321
1.028
0.254
1.003
1.014
Te
1.139
1.470
1.536
1.799
1.833
1.895
1.921
1.965
4.000
4.000
4.000
4.000
4.000
4.000
4.000
4.000
ΣX
Se
10.8658.637 11.146 10.971 11.518 10.752 11.708 10.919
S
1.925
3.902
1.686
1.658
1.282
1.662
1.227
1.934
ΣS+Se
12.790 12.539 12.833 12.629 12.800 12.414 12.935 12.853
Coefficients of empirical formula calculated on the basis 4 apfu = Sb + Bi + Te

up to 2 apfu (Biagioni et al. 2020a, 2022). Associatedhakite-(Hg) shows Me2+ contents in the range 1.22–1.56
apfu (Fig. 5a); members with Te < 1 and Me2+ in the range
0.37–1.01 apfu (Fig. 5a) probably correspond to the notyet approved end-member “hakite-(Cu)” with variableratios Cu+/Cu2+.
The determined Sb/(Sb + As) ratios do not correlatewith Te contents (Fig. 5b). Both Sb- (prevailing) andAs-dominant members have been observed in the material studied. The range of SeS–1 substitution is limited to3.90 apfu S (Fig. 5c).

5. X-ray crystallography
Powder X-ray diffraction data could not be collected
due to the paucity of available material. Consequently,
powder X-ray diffraction data, given in Tab. 4, were
calculated through the software PowderCell 2.3 (Kraus
and Nolze 1996) on the basis of the crystal structure
model (our stoichiometry and unit-cell parameter, atom
coordinates from stibiogoldfieldite, Biagioni et al. 2022).
A short prismatic fragment of stibioústalečite, 30 ×
24 × 12 μm in size, extracted from the polished section

0.30
0.00
0.00
0.00
0.00
34.18
8.94
0.50
38.35
12.71
3.31
98.29
0.062
5.938
6.000
6.034
0.000
0.000
0.000
0.000
6.034
1.634
0.149
2.217
4.000
10.8102.298
13.108

0.93
0.00
0.05
0.07
0.51
34.51
5.56
4.99
41.22
10.16
3.59
101.59
0.180
5.820
6.000
5.500
0.000
0.005
0.022
0.053
5.580
0.952
1.388
1.660
4.000
10.8822.334
13.216“arsenoústalečite”
1.54
0.56
0.24
0.00
0.09
0.23
0.00
0.00
0.00
0.00
0.08
0.11
0.22
0.12
0.00
36.46
36.28
35.45
4.81
4.71
5.72
4.78
5.44
3.71
37.92
38.19
39.60
10.42
10.44
11.65
3.54
4.04
3.27
99.69
99.95
99.98
0.309
0.108
0.047
5.691
5.892
5.953
6.000
6.000
6.000
6.716
5.933
5.929
0.000
0.033
0.088
0.000
0.000
0.000
0.000
0.025
0.036
0.024
0.012
0.000
6.740
6.004
6.053
0.854
0.801
1.001
1.380
1.504
1.055
1.766
1.695
1.945
4.000
4.000
4.000
10.385 10.018 10.682
2.388
2.610
2.172
12.773 12.628 12.854

0.31
0.40
0.00
0.00
0.00
34.73
5.26
3.77
40.34
11.66
2.61
99.08
0.062
5.938
6.000
5.885
0.155
0.000
0.000
0.000
6.040
0.935
1.089
1.977
4.000
11.0521.761
12.813and analyzed using an electron microprobe (Fig. 2), wasmounted on glass fiber and examined with an Rigaku
SuperNova single-crystal diffractometer equipped withan Atlas S2 CCD detector and a microfocus MoK α
source. Data reduction was performed using CrysAlisPro
Version 1.171.39.46 (Rigaku 2019). The cubic [spacegroup: I4̄ 3m (#217)] unit-cell parameter determined fromsingle-crystal data is a = 10.828(4) Å, V = 1269.6(9) Å3
and Z = 2. The single-crystal X-ray diffraction data werecorrected for Lorentz factor, polarization effect (Rigaku
2019) and for absorption (Gaussian type in Jana2006).
The attempts to refine the structure of stibioústalečite(using the Jana2006 program, Petříček et al. 2014) fromthese data resulted only in a very problematic refinement due to extremely poor diffraction intensities, Rint =21.4 %. During the refinement, severe correlations, theimpossibility to let the occupancies be refined freely,large atomic displacement parameters, and several additional issues (significantly large errors on a few variables,such as on inversion twin fractions) appeared. Therefore
we do not present the results of refinement here and thecollected single crystal diffraction data were used for the
space group assignment and refinement of the unit-cellparameter of stibioústalečite.
293

Jiří Sejkora, Jakub Plášil, Emil Makovicky

6. Discussion andconclusions

2.5
stibioústalečite - grain used for SCXRD
stibioústalečite - other grains"arsenoústalečite""hakite-(Cu)"hakite-(Hg)Te (apfu)

2.0
1.5
1.0
0.5
0.0

(a)
0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Hg+Fe+Zn+Cd (apfu )stibioústalečite - grain used for SCXRD
stibioústalečite - other grains"arsenoústalečite"

2.4
2.2

Te (apfu)

2.0
1.8
1.6
1.4
1.2
1.0

(b)

0.8
0.0

0.2

0.4

0.6

0.8

1.0

Sb/(Sb+As)
stibioústalečite - grain used for SCXRD
stibioústalečite - other grains"arsenoústalečite"4

S (apfu)

3

2

1

(c)
8

9

10

Se (apfu)
294

11

12

An unambiguous determinationof stibioústalečite as a member of the tetrahedrite group isbased on its chemical composition (stoichiometry), symmetry
and unit-cell parameter refinedfrom single-crystal X-ray diffraction data. The increase ofunit-cell parameter (due to theSeS–1 substitution) for stibiogoldfieldite (Biagioni et al. 2022)/
stibioústalečite (this paper), 0.48
Å, is comparable with the valueof 0.41 Å, observed in the caseof tetrahedrite-(Hg) (Rožňava,Biagioni et al. 2020b)/hakite(Hg) (Škácha et al. 2016).
The role of tellurium in the
crystal structure of tetrahedrite
group minerals was recently reviewed by Biagioni et al. (2020a;
2022). Kato and Sakurai (1970)
and Kalbskopf (1974) realized that Te does not substitutefor S (as believed earlier, e.g.,
Nowacki 1969) but behaves likeAs and Sb in the tennantite–tetrahedrite series, as proposedby Lévy (1967). In addition,
Kalbskopf (1974) observed theappearance of vacancies at thetrigonally coordinated M(2) site.
Similar results were later foundby Dmitrieva et al. (1987) andPohl et al. (1996).
Later, several authors (e.g.,
Novgorodova et al. 1978; Kase
1986; Knittel 1989) proposedthat the accommodation of
Te 4+ (up to 2 Te apfu) in the
crystal structure of a tetrahedrite group mineral is possible through an increase of Cu +Fig. 5 Compositional variation of Te-bearing tetrahedrite-group minerals fromÚstaleč. a – The (Zn + Fe + Zn + Cd) vs.
Te (apfu) graph for Te-bearing tetrahedrite-group minerals. b – The Sb/(Sb + As)
vs. Te (apfu) graph for minerals of ústalečite series. c – The Se vs. S (apfu) graphfor minerals of ústalečite series.

Stibioústalečite, a new tetrahedrite group mineral from Ústaleč

Tab. 4 Calculated X-ray powder diffraction data for stibioústalečite

Tab. 5 Crystal and experimental data for stibioústalečite

Icalc.
dcalc.
hkl
0.9
5.41402
0
0
4.9
4.42052
1
1
9.6
3.82832
2
0
6.3
3.42413
10
100.0
3.1258222
10.9
2.893932
1
6.7
2.70704
002.3
2.55223
3
0
9.3
2.5522411
1.3
2.42124
20
1.5
2.30853
32
2.8
2.2103422
4.2
2.12365
1
0
3.4
2.12364
3
1
11.1
1.976952
1
71.1
1.914144
0
2.4
1.8570433
7.9
1.7565611
1.3
1.75655
32
2.9
1.71216
2
0
33.4
1.63246
2
2
1.1
1.562944
4
1.6
1.53135
50
2.8
1.531354
3
1.0
1.53137
10
1.3
1.47356
3
3
9.1
1.35358
00
1.4
1.3328554
1.4
1.3328741
5.7
1.2942
6
5
3
Intensity and dhkl were calculated using the software PowderCell2.4(Kraus and Nolze 1996) on the basis of the crystal structure model (ourstoichiometry and unit-cell parameter, atom coordinates of stibiogoldfieldite, Biagioni et al. 2022). Only reflections with Icalc > 1 are listed.
The eight strongest reflections are given in bold.

Crystal data
Crystal size (mm3)
Cell setting, space groupa (Å)
V (Å3)Z
Data collection
Radiation, wavelength (Å)
Temperature (K)θmax (°)
Measured reflections
Unique reflections
Reflections with Fo > 3σ(Fo)Rint
Rσcontent (and minor Ag + ) from 10 to 12 apfu, according to the substitution M(1) Me 2+ + X(3) (Sb/As) 3+ =M(1)Cu + + X(3)Te 4+, where Me = Fe, Zn, Hg and others.
For Te contents between 2 and 4 apfu, the charge balance is maintained through the creation of vacancies at
the M(2) site, according to the substitution mechanism
M(2)Cu+ + X(3)(Sb/As)3+ = M(2)□ + X(3)Te4+. A discussion of thecrystal chemistry of the substitutional series between tetrahedrite/tennantite series and goldfieldite is reported in
Trudu and Knittel (1998). Makovicky and Karup-Møller
(2017) performed syntheses of the complete tetrahedrite–goldfieldite and tennantite–goldfieldite sections andreviewed recently published chemical analyses.
Increased Se-contents with a maximum of 3.0 apfu
are known in Te-rich members of tetrahedrite group only
from samples from the epithermal Au deposits at Kamchatka, Russia (Spiridonov and Okrugin 1985; Pohl etal. 1996; Spiridonov et al. 2014), and from the Wild Dog

Range of h, k, l

0.030 × 0.024 × 0.012
Cubic, I4̄ 3m
10.828(4)1269.6(9)2MoKα, λ = 0.71073
297.29(18)
29.3
3776
3761
632
0.214
0.335
13 ≤ h ≤ 13,−13 ≤ k ≤ 10,−9 ≤ l ≤ 14

epithermal Au system on Bougainville Island, Papua New
Guinea (Noviello 1989). The experiments at 340 °C byde Medicis and Giasson (1971) on the system Cu–Te–Se
failed to produce the Se-bearing analogs of goldfieldite,Trudu and Knittel (1998) could not assess whether complete Se-for-S substitution exists in goldfieldite.
The classification of Te-bearing minerals of the tetrahedrite group has been debated for a long time anddifferent nomenclatural approaches have been proposed.
When establishing the nomenclature of tetrahedrite
group, Biagioni et al. (2020a) recognized this inconsistency and based their revision on three end-member
formulas for Te-bearing tetrahedrite-group minerals,i.e., Cu6Cu6(Sb2Te2)S13, Cu6Cu6(As2Te2)S13, and (Cu4□2)
Cu 6Te 4S 13. In order to avoid further confusion, they
proposed to use the name goldfieldite to indicate theend-member composition (Cu4□2)Cu6Te4S13 = Cu10Te4S13,
in agreement with Moëlo et al. (2008). New names areto be proposed for the other two end-member (sensu
Hawthorne 2002) compositions. In the tetrahedrite/tennantite–goldfieldite series, the following boundaries were
proposed by Biagioni et al. (2020a):(1) tetrahedrite/tennantite, with 0 < Te (apfu) < 1;(2) new names, for the compositions with 1 < Te (apfu) < 3.
Two different names (e.g., stibiogoldfieldite; arsenogoldfieldite) should be applied, taking into accountthe dominant trivalent constituent;(3) goldfieldite, with 3 < Te (apfu) < 4.
The proposed new mineral s tibioústalečite,Cu6Cu6(Sb2Te2)Se13, is evidently a Se-analog of stibiogoldfieldite (Biagioni et al. 2022), and therefore, following the classification of Biagioni et al. (2020a), we
propose the same type of scheme for possible membersof the ústalečite series:(1) hakite/giraudite, with 0 < Te (apfu) < 1;295Jiří Sejkora, Jakub Plášil, Emil Makovicky(2) new names, with 1 < Te (apfu) < 3. Two different names – stibioústalečite, which is described here, and apotential “arsenoústalečite” should be applied, taking
into account the dominant trivalent constituent;(3) possible “ústalečite”, with 3 < Te (apfu) < 4.
Acknowledgments. The study was financially supported by the Ministry of Culture of the Czech Republic(long-term project DKRVO 2019-2023/1.II.d; National
Museum, 00023272). We acknowledge CzechNanoLab Research Infrastructure supported by MEYS CR(LM2018110) for financial support for the collection ofdiffraction data. The referee, Pavel Škácha, and the handling editor, František Laufek, are highly acknowledged
for comments and suggestions that helped to improvethe manuscript.

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